IN HIS LATEST BOOK, The Lost Soul of American Politics, John Diggins tries to explain why our political culture has been dominated by liberalism, why this has led many intellectuals to be alienated from politics, and above all, why American politics seems to have lost its moral vision since the death of Lincoln. Although this is a book on politics, his answers all have to do with religion, in particular with Calvinism. Diggins believes that liberal individualism “seemed to leave America without a sense of moral community,” and that liberal pluralism—the licensed competition of self-interested groups—left her “without a sense of national purpose.” But he is also aware of recent writers who wrongly try to deny America’s liberal heritage altogether.  Thus his project is simultaneously to reassert America’s liberal traditions while showing that liberalism itself has had roots in a morally serious Calvinism that, fully developed in Lincoln, became “the conscience of liberalism.”